This invention relates generally to a tying machine as used for tying a group or bundle of items, for examples, celery, asparagus, broccoli and the like, and more particularly to a twist tying machine which operates on compressed air and without the use of electrical devices, complex camming and other timing mechanisms. Prior art patents teach the development of machines which effectively apply a tie wire about products such as asparagus, broccili, celery stalks, to protect those products in transit prior to retail sale. The tie is a malleable wire sandwiched between two strips of paper secured together, for example, with adhesive, to form a flat tie ribbon. After a snug loop of ribbon is formed around the product, the ends of the ribbon are clamped. These clamped ends are then rotated about a central axis producing permanent twists in the tie ribbon whereby the loop and product are held together. In the known manner, the ribbon can be untwisted by the purchaser of the product and retwisted when it is desired to reapply the ribbon. These procedures have become most familiar to consumers in this country with twist ties being used on many products, not only to hold the above-mentioned products together but to provide closures for paper and plastic bags containing food stuff such as bread, and in larger sizes for bags used, for example, for containing potatoes, onions, etc. Many operational steps are required to apply a twist tie, in the form of a wire/paper ribbon. In the past, complex machinery has been designed to effect performance. These machines, as illustrated, for examples, in U.S. Pat. Nos. 3,318,230, issued May 9, 1967; 3,428,096, issued Feb. 18, 1969; 3,898,924, issued Aug. 12, 1975, and 4,177,842, issued Dec. 11, 1979, are machine constructions relying on complex mechanisms, electrically driven in some instances, and generally using cam devices to provide sequential motions necessary to the procedural steps in applying a twist tie ribbon to the product. Each progressive patent teaches an improvement in performance and simplification in structure, however, reliance on cams for critical motions, for example, in gripping the ends of the ribbon prior to twisting, and in cutting the ribbon after gripping is prevalent. Endless belt chain drives, pulleys, complicated linkage systems are not uncommon and the need for adjustment for operation and to compensate for temperature variations and for wear is relatively frequent. Use of both a forward feed drive for the ribbon and also an independent reverse feed drive for tightening the ribbon about the bundle is also disclosed in the prior art, adding to complexity.
What is needed is a twist tying machine which is simple and reliable in construction, and reducing the total number of parts, and the need for precise timing and critical mechanical interrelationships requiring frequent adjustment.